**1 人解决**，1 人已尝试。

**1 份提交通过**，共有 3 份提交。

**9.3** EMB 奖励。

**单点时限: **2.0 sec

**内存限制: **256 MB

Write a program that:

1.reads the description of a board and numbers of squares on which pieces are placed initially.

2.decides if player B can catch player A and if so, computes how many turns he needs (we assume that both players play optimally);

3.writes the result.

In the first line of the input file GON.IN there are four integers n, m, a and b separated by single spaces, where 2<=n<=3000, n-1<=m<=15000, 1<=a,b<=n and a <b. These are (respectively): the number of squares of the board, the number of adjacent (unordered) pairs, the number of the square on which the piece of player A is placed, the number of the square on which the piece of player B is placed. In each of the following lines there are two distinct positive integers separated by a single space, which donote numbers of adjacent squares.

In the first and only line there should be:

1.one word NIE (which means NO in Polish), if player B can not catch player A, or

2.one integer - the number of turns needed by B to catch A (if B can catch A).

Input

9 11 9 4 1 2 3 2 1 4 4 7 7 5 5 1 6 9 8 5 9 8 5 3 4 8

Output

3

**1 人解决**，1 人已尝试。

**1 份提交通过**，共有 3 份提交。

**9.3** EMB 奖励。

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